docs: def show_attrs(key, calc_id=-1):
      """
      Show the attributes of a HDF5 dataset in the datastore.
      """
      ds = util.read(calc_id)
      try:
          attrs = h5py.File.__getitem__(ds.hdf5, key).attrs
      except KeyError:
          print('%r is not in %s' % (key, ds))
      else:
          if len(attrs) == 0:
              print('%s has no attributes' % key)
          for name, value in attrs.items():
              print(name, value)
      finally:
          ds.close()